Tuesday, October 18, 2016

When I was a young professor, I looked down my nose a bit at
professors who only published review papers, leaving all the empirical papers
to their students. Now that I am a middle-aged professor, it feels like all I
do these days is write review papers. Just these last few years, I have written
(or helped to write) reviews for Heredity, Journal of Heredity, Philosophical
Transactions of the Royal Society B, Evolutionary Applications (2), Science,
Annals of the New York Academy of Sciences, Trends in Ecology and Evolution,
and others. I haven’t written a true empirical paper since 2013, when I
published two. Moreover, even my forthcoming book can be thought of as one long
review paper.

A major reason for this shift is that “older” Professors are
better known and so are increasingly asked to write reviews. Indeed, most of
the review papers listed above were invited by the journals – and the others
were requests to participate from younger researchers. As all of the requests
came from friends or colleagues, were in good journals, and gave us the
opportunity to say pretty much what we wanted, I accepted them. Of course, I
also enjoyed writing them and I hope they stimulate new ideas and research
interest. Or could this simply be lipstick on a pig.

Review papers have been criticized for not generating new
knowledge, which presumably would be much better than simply summarizing
existing knowledge. Indeed – on this blog – one post criticized review papers in
eco-evolutionary dynamics for being more frequent than empirical papers in
eco-evolutionary dynamics. The basic argument is that people should stop
spending their time writing reviews and should instead go out and collect new data
and run new experiments. Otherwise, progress in science will be stifled – or
perhaps more appropriately it will be like one of those “bubbles” they talk
about for sub-prime mortgages. Or a house of cards. Etc.

So what are review papers good for then – and should you
take the time to write one? I would argue that – while all of the above is true
– review papers (some of them anyway) are very valuable and should be deployed
early and often in your career.

1. One benefit of review papers is that they bring together and
synthesize a large amount of literature. So many papers are being published
these days that it is impossible to keep on top of all (or even most) of them.
Review papers thus become great ways to see what is in the literature in a
single reading and can help to identify empirical papers that you might not
have known about.

2. Another potential benefit of review papers is that they
often allow more subjectivity in interpretation and more speculation. Writing an
empirical paper can constrain you to only asserting conclusions that are
strongly supported by the data. This constraint is good, of course, because
empirical papers are specifically claiming that original data support a
conclusion. At the same time, the constraint can be limiting in that empirical
data might inspire new ideas that are not strictly supported by the data, yet
are nevertheless good ideas that can move the field forward.
Reviews/syntheses/opinions are great places to get these bold new ideas out
there even if they aren’t yet supported by (much) data.

More pragmatically, review papers are great ways for younger
researchers to increase their exposure. In some cases, a student can write an
excellent series of empirical papers that don’t gain much attention, simply
because so many papers are out there. Review papers often gain more attention
(or at least exposure through citaitons) and can thereby help a young
researcher become known as an expert and an original thinker in a particular
area, and they can also bring attention to that researcher’s empirical papers.
This pragmatic benefit was certainly the case for me, where a review paper I
published just after my PhD (Hendry and Kinnison 1999 - Evolution) helped to
promote the importance of contemporary (rapid) evolution and remains one of my
highest-cited papers (495 citations on Web of Science, 682 citations on Google Scholar).

Citations to all of my papers by year of publication (to 2010). Comments, responses, etc. are omitted.

But perhaps now that I am getting longer in the tooth, I
should stop writing these things – or at least so many of them. Maybe if I
stopped writing so many, I could write more and better empirical papers. Maybe
it is all a big trade-off and I have shifted too far to one pole. These sorts
of questions got me to wondering, what would my CV look like if I subtracted
all of my review papers? So I did precisely that. I downloaded Web of Science
data for all of my papers, subtracted commentaries, and divided them into
review papers and primary data papers.

Review papers are clearly boosting my stats or, more importantly,
increasing awareness of my work. Yet the above table isn’t exactly a fair
comparison given that writing review papers presumably reduces the number of empirical
papers I can publish. So, on the charitable assumption that I could write roughly
one empirical paper for each review paper, I simply replaced my 29 review
papers with the average empirical paper (ignoring date of publication). That
is, I assumed that my 29 review papers were replaced with 29 copies of my
average empirical paper, yielding 149 total papers with 7181 citations and an h
index of 48.

To continue the absurdity; what if all my papers
were review papers? Here I replaced all 120 empirical papers with the average
review paper. The stats are shown below and – if all else was equal and if
citations were all that mattered – I should simply publish review papers.

Of course all else is not equal. For instance, my tendency
to be invited to provide reviews might require a firm empirical footing based
on original data. Alternatively (or additionally), my empirical papers might be
cited more heavily because of the exposure brought by reviews. Or both, which
indeed is my point. Not only are reviews good for the reasons described above
but they also form a nice conceptual and promotional complement to related data
papers.

In short, I strongly recommend
that advanced PhD students and postdocs should write review papers. Those
papers can strongly influence your research field. They will be cited. They
will simulate your own thinking. They will enhance your empirical research.

As for what makes a good review paper, I have a couple of
suggestions:

1. Meta-analyses are much better than conceptual thought
pieces. Indeed, I have included meta-analyses in my empirical category above.
Of course, the best reviews would be both – conceptual and meta-analytical.

2. Don’t just review the evidence, present new ideas and advance
new hypotheses. Although you can make some hay from rehashing previous review
topics, the way to make a real influence is to come up with new ideas and
review new topics.

The day after writing the above, I (by
coincidence) was a guest editor at the annual meeting of the board of the
Annual Review of Ecology, Evolution, and Systematics, where I agreed to write
another paper. And, of course, I have another paper in preparation for Trends
in Ecology and Evolution, and several other reviews papers beyond those. So
this trend will clearly continue for awhile longer. I am starting to really
miss those empirical papers!